The invention relates to an ultrasonic motor, especially the prevention of noise generated in the ultrasonic motor and the prevention of heat generated due to mechanical loss from being transmitted to an ultrasonic vibrator.
Ultrasonic motors are known in the art and broadly classified into travelling-wave types and standing-wave types. The principle of operation of the standing-wave type ultrasonic motor is to abut a moving member, with specified pressure, against an ultrasonic vibrator excited substantially in elliptical movement so as to drive the moving member by a frictional force between contact points on the ultrasonic vibrator, which are elliptically vibrating, and the moving member.
An example of such motors is disclosed in Japanese Patent Application No. H1-46866. As shown in FIG. 3, a linear ultrasonic motor 1 includes an ultrasonic vibrator 3 attached to a yoke 2. At one end of the vibrator 3, there is formed a drive unit 4. A moving member 5 is pressed against the drive unit 4 by a rubber roller 6. The moving member 5 is supported by linear bearings 7a and 7b, which are secured to the yoke 2. When the vibrator 3 is excited, the moving member 5 moves in a direction shown by an arrow A, being driven by elliptical vibration. This force is caused by frictional force between the drive unit 4 and the moving member 5.
In the above ultrasonic motor, a great pressing force is required for obtaining a large output on the sliding surface between the output end portion of the ultrasonic vibrator and the mover. In the ultrasonic motor, however, which utilizes substantially an elliptical vibration, velocity difference between the ultrasonic vibrator and the mover are inevitably produced resulting in the generation of noise or unnecessary vibration due to repetition of high-speed sliding.
Furthermore, most of the driving loss is mechanical loss on the sliding surface between the ultrasonic 3 and the moving 5 member. This lost energy becomes heat. Subsequently, the electromechanical conversion element, which is the source of exciting the ultrasonic vibrator, comprising piezoelectric elements or the like, is heated, resulting in deterioration of its performance or a change in the resonance frequency of the vibrator itself.
Wherefore, one object of this invention is to prevent the above-described noise or unnecessary vibration originating from friction on the sliding surface in standing wave ultrasonic motors.
Another object of this invention is to provide a standing wave ultrasonic motor which enables stabilized and high efficiency operation for long hours by preventing the heat produced by mechanical loss from being transmitting into the ultrasonic vibrator.
Other objects and benefits of the invention will become apparent from the detailed description which follows hereinafter when taken in conjunction with the drawing figures which accompany it.